Very often I see on the web many flash websites very amazing for their animation in flash. For example, in monster template you can see the paper's animation like that: http://www.templatemonster.com/flash-templates/26676.html Watch the BEST DESIGN STUDIO animation... very excellent! These animations aren't made with flash, but with a software from which to export a swf file that contains a sequence of shapes. Do you have any idea about that software? What is it? It seems to work in 3d, but the objects moved are always planes and not 3d models.

Flash CS4 Professional has some 3D characteristics as well as character animation characteristics (such as IK joint solvers) which are found in 3D packages. It is possible that this was done in a 3D program or even After Effects and exported to Flash within the Creative Suite. 3D planes do not have to have depth but will animate the way you have shown in the "monster template".

These animations are indeed made with flash. You can easily make those animations with shape tweens though you will need some artistic skills in it. I do not think they use any 3D libraries because they can easily be made with shape tweens. Applications that do such animations are mostly also made with flash. You can do these animations too, you just need practice and patience